Preheat the oven to 350 degrees.
Spray a 2-quart casserole dish with nonstick spray.
Heat the oil in a large skillet over medium heat; add the butter. Saute the squash and onion until soft.
Transfer to a bowl and stir in the cheese and sour cream.
Place in the prepared casserole dish and
sprinkle the cracker crumbs evenly over the top.
Pour melted butter over the cracker crumbs.
Bake for 25-30 minutes or until the top is golden and bubbly.